Seu ip deve estar na br0, eth0 não terá ip. Algo parecido com isto:
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
iface eth0 inet manual
auto br0
iface br0 inet static
address xxx.xxx.xxx.xxx
netmask xxx.xxx.xxx.xxx
gateway xxx.xxx.xxx.xxx
bridge_ports eth0
bridge_stp off
bridge_fd 0
bridge_maxwait 0